The invention relates to a method and an arrangement for establishing a mobile-terminating call in a mobile communications network when the call is received from a calling party via a fixed network without any signalling support for carrying information on the protocol employed by the calling party.
Present-day mobile communications systems provide the subscribers, in addition to standard speech transmission, with a variety of data transfer features. The data services usually employ a certain specified communication protocol within the mobile network. In the pan-European digital mobile communication system GSM (Global System for Mobile Communications), for instance, a CCITT V.110-based, UDI coded rate adaptation protocol is employed, and, in addition, a radio link protocol (RLP) is employed in non-transparent services. A digital connection from a mobile network to a fixed network, such as an ISDN (Integrated Services Digital Network) or a public switched telephone network PSTN, may employ different kinds of protocols. Examples of such protocols are the rate adaptation protocols CCITT V.110 and V.120 of the ISDN network.
An important feature related to data transfer services are adaptation functions for adapting the internal data connection within the mobile network to the protocols employed by the terminal equipments and other telecommunications networks. Typically, the adaptation functions are a Terminal Adaptation Function TAF at the interface between a mobile station and a data terminal connected thereto, and an Interworking Function IWF at the interface between the mobile network and another telecommunications network.
Mobile networks are expected to provide a wide range of data services of various kinds which support the commonest data transfer protocols of fixed telecommunications networks. Consequently, a separate IWF is also required for each data transfer protocol. The mobile network must know which data transfer protocol the terminal equipments wish to employ in each call in order that it would be able to select the correct IWF.
In a mobile-originating call (MOC) the mobile station signals the information on the protocol it wishes to be employed towards the fixed network and the called party. In GSM mobile communications system, for instance, the information on the desired protocol is in a Bearer Capability Information Element (BCIE) in a setup message. On the basis of this information, the IWF is configured to provide a suitable interworking function between the mobile network and the telecommunications network. In case signalling that supports transmitting the protocol information is employed on the entire connection between the mobile network and the called party, the information is also transmitted to the called party. The required signalling support is provided e.g. in ISDN networks (Integrated Services Digital Network). If such signalling support is not provided, it is the responsibility of the calling subscriber to select the correct protocol, that is, the calling subscriber must know the protocol of the called subscriber and select the protocol of the IWF accordingly. Signalling support is not available e.g. in the conventional public switched telephone network PSTN.
A mobile-terminating call (MTC) is more problematic. In case the required signalling support is available on the entire connection between the calling party and the mobile network, the protocol parameters of the calling subscriber are transmitted to the mobile network, which may configure the IWF according to them. In practice, however, signalling support is not always available over the entire connection. This is the case, for instance, when a call originates from the PSTN or has been routed via the PSTN. When the signalling support is not available, the mobile network should be able to obtain the information on the protocol required by the call in some other way.
A prior art approach to the problem is a Multi Numbering Scheme, in which a mobile subscriber has as many directory numbers (MSISDN) as he has different services to which he wishes to receive incoming calls. In accordance with the multinumbering scheme, the calling subscriber dials the directory number of the mobile subscriber according to the desired service. In the GSM system, the services of the subscribers are determined in a subscriber""s home location register (HLR), in which other subscriber information is also stored permanently. The HLR is also used for storing information on the mapping between the directory numbers and the services of the subscribers. In the HLR, a specific BCIE element indicating the type of a call and the network resources and the protocol required for the call is also linked with the Mobile Subscriber ISDN Number (MSISDN). The IWF may be configured according to this information. According to the present recommendations, a subscriber has a separate MSISDN number for the V.110 protocol and a separate MSISDN number for the V.120 protocol.
For the network operator and the mobile subscribers, such a vast number of services causes confusion and trouble. In order for the mobile subscriber to be able to carry out and receive calls requiring different protocols, he must subscribe to several different bearer services from the network operator. From the point of view of the network operator, it is in turn problematic that each user should require a plurality of directory numbers, which wastes the number space of the network. Furthermore, determining the services in the network databases consumes database capacity. The multinumbering scheme is thus a working, yet a poor solution.
It is an object of the invention to provide a method and arrangement that allow protocol adaptation between the mobile communications system and the fixed network more efficiently as compared with the present multinumbering scheme in a case where no signalling support is provided, thus saving the number space and database capacity.
This is achieved with a method for establishing a mobile-terminating data call when the call is received from the calling party via a fixed network without signalling support carrying the information on the protocol employed by the calling party. The method is characterized by
receiving a call to a directory number of a subscriber, said directory number being assigned to a data service employing two or more alternative protocols towards the fixed network,
retrieving from the subscriber data a service definition linked with said directory number, the protocol parameter of said definition having a neutral value or a value that is interpreted as neutral,
assigning an interworking function resource in accordance with said service definition, omitting the definition of the protocol due to said neutral value or the value that is interpreted as neutral,
monitoring by means of the assigned interworking function resource the traffic channel received from the fixed network,
identifying the protocol employed by the calling party on the basis of signalling characteristic thereof,
configuring said assigned interworking function resource to employ said identified protocol towards said calling party.
The invention also relates to providing an arrangement for establishing a mobile-terminating data call in a mobile communications network when the call is received from the calling party via a fixed network without signalling support carrying the information on the protocol employed by the calling party. The arrangement is characterized by
the subscriber database of the mobile communications network having one directory number defined for a subscriber""s data service that employs two or more alternative protocols towards the fixed network, the protocol parameter of a service definition linked with said directory number having a neutral value or a value that is interpreted as neutral,
the mobile network being arranged, in a mobile-terminating call made to said directory number, to assign an interworking function apparatus according to the service definition, but to omit the configuration of the protocol employed towards the fixed network due to the neutral value of said protocol parameter or the value that is interpreted as neutral,
said assigned interworking function apparatus (IWF) being arranged to monitor a traffic channel received from the fixed network, to identify the protocol employed by the calling party (TE) on the basis of signalling characteristic thereof, and to configure itself to employ said identified protocol towards said calling party.
It is yet another aspect of the invention to provide an interworking function apparatus for achieving a protocol adaptation between a mobile communications network and a fixed network when a call is received from the calling party via the fixed network without any signalling support carrying the information on the protocol employed by the calling party. The apparatus is characterized by
the interworking function apparatus being arranged, in a mobile-terminating call, to assign interworking function resources according to the service definition obtained from the subscriber database, but to omit the configuration of the protocol employed towards the fixed network if the protocol parameter of said service definition has a neutral value or a value that is interpreted as neutral,
the interworking function apparatus being arranged to monitor a traffic channel received from the fixed network, to identify the protocol employed by the calling party on the basis of signalling characteristic thereof, and to configure said assigned interworking function resources to employ said identified protocol towards said calling party.
In the invention, a service is assigned only one directory number which is common to all the protocols employed by the service. In the service definition linked with this directory number, the protocol identifiers are neutral (undefined) in value or interpreted as neutral. When the interworking function (IWF) of the mobile network receives, in case of a mobile terminating data call, a protocol identifier which is neutral or interpreted as neutral, it does not attempt, after being switched to the line, to synchronize itself towards the fixed network according to any protocol, but it monitors the traffic channel received from the fixed network in order to identify the protocol employed by the calling terminal equipment. The IWF, however, synchronizes the internal data connection within the mobile network in the specified way in the direction of the mobile station. After identifying the protocol of the calling terminal equipment, the IWF starts to operate in the manner required by the identified protocol. After setting up a data link, the IWF signals the status of the traffic channel to the mobile station in the usual way, and data transmission may begin.
Identifying the protocol is based on detecting synchronization or signalling characteristic thereof. The CCITT V.110 protocol may be identified by means of a V.110 synchronization frame. After identifying the V.110 synchronization frame, the IWF itself starts transmitting V.110 synchronization frames to the fixed network. The CCITT V.120 protocol may also be identified by means of a V.120 frame flag, in addition to which the identification may be confirmed by means of a link setup message. After identifying a V.120 frame flag, the IWF itself starts transmitting frame flags to the fixed network, and after identifying the link setup message, it acknowledges the message etc.